The role karyotypic rearrangements in raciation and speciation of Australian grasshoppers is being studied, using techniques such as experimental hybridization, tritiated autoradiography and Giemsa banding. Particular attention is being paid to the genetic system of a parthenogenetic species in which there is no genetic recombination. This species has been successfully crossed with males of related bisexual species to give triploid progenies which include males and females. Isozyme studies indicate that the populations of the parthenogenetic species are genetically very uniform, enzymic variants being rare. Future work planned for 1974 includes further studies of inverted chromosome sequences which are known to differ in their DNA replication pattern from the standard sequence (in the species Keyacris scurra) and much further work on the triploid hybrids between the parthenogenetic species and at least three related bisexual species. Studies of isozyme polymorphism in the bisexual species will also be carried out for comparison with the data already obtained on the parthenogenetic one.